Total synthesis of (-)-hennoxazole A

An enantioselective, convergent, total synthesis of the antiviral marine natural product (-)-hennoxazole A has been completed in 17 steps, longest linear sequence, from serine methyl ester and in 9 steps from an achiral bisoxazole intermediate. Elaboration of a thiazolidinethione allowed for rapid assembly of the pyran-based ring system. Key late-stage coupling was effected by deprotonation of the bisoxazole methyl group, followed by alkylation with an allylic bromide side chain segment. [structure: see text]     

Total synthesis of (-)-hennoxazole A

An enantioselective, convergent total synthesis of the antiviral marine natural product (-)-hennoxazole A is completed in 14 steps (longest linear sequence) from commercially available 4-methyloxazole-2-carboxylic acid. Synthesis of the C(1)-C(15) pyran/bisoxazole fragment takes advantage of an aldol-like coupling between a dimethyl acetal and an N-acetylthiazolidinethione for the direct, stereoselective installation of the C(8)-methoxy-bearing stereocenter. A one-pot acetoacetate acylation/decarboxylation/cyclodehydration of another elaborate thiazolidinethione allows for rapid assembly of the pyran-based ring system. Synthesis of the C(15)-C(25) skipped triene side chain fragment makes use of a [2,3]-Wittig-Still rearrangement for efficient installation of the trisubstituted Z-double bond. Key late-stage coupling of the two fragments is effected by deprotonation of the methyl group on the bisoxazole system using lithium diethylamide, followed by alkylation with an allylic bromide side chain segment to form the C(15)-C(16) bond.     

Total synthesis of the marine natural product (-)-clavosolide A

[Structure: see text] The total synthesis of the marine metabolite clavosolide A is reported which confirms the structure and absolute configuration of the natural product as the symmetrical diolide glycosylated by permethylated D-xylose moieties, 2.     

Total synthesis of the marine natural product (-)-clavosolide A. A showcase for the Petasis-Ferrier union/rearrangement tactic

[Structure: see text] The total synthesis of the marine diolide (-)-clavosolide A has been achieved in 17 steps (longest linear sequence) from commercially available crotonaldehyde exploiting the Petasis-Ferrier union/rearrangement tactic to construct the requisite aglycon monomer. A one-pot esterification/lactonization employing the Yamaguchi protocol, followed by bis-glycosidation, furnished (-)-clavosolide A.     

Total synthesis of a diastereomer of the marine natural product clavosolide A

The first total synthesis of the reported structure of the sponge metabolite clavosolide A is described using a Prins cyclisation to assemble the tetrahydropyran core followed by manipulation of the side-chain, dimerisation and finally glycosidation.     

Total synthesis of the chlorinated marine natural product dysamide B

[Structure: see text] Two approaches to the synthesis of (2S,4S)-5,5-dichloroleucine are compared, and the parent amino acid was used in the first total synthesis of the polychlorinated marine natural product, dysamide B. A key step was the lead tetraacetate-mediated decarboxylation of an alpha,alpha-dichloro acid in the presence of 1,4-cyclohexadiene to generate the dichloromethyl group.     

Total synthesis of (-)-minquartynoic acid: an anti-cancer,anti-HIV natural product

[structure: see text] The tetraacetylenic compound, (S)-minquartynoic acid (1), is synthesized in seven linear steps and 17% overall yield from commercially available azelaic acid monomethyl ester. The key step is a one-pot three-component Cadiot-Chodkiewicz reaction to construct the tetrayne unit without using either a diyne or a triyne intermediate.     

Total synthesis of the cytostatic marine natural product dibromophakellstatin via three-component imidazolidinone anellation

The tetracyclic pyrrole-imidazole alkaloid dibromophakellstatin from the marine sponge Phakellia mauritiana has been synthesized within seven steps from pyrrole in an 18% overall yield. The key step is a three-component assembly of a tricyclic enamide, a nitrene, and a carbamoyl building block, affording the imidazolidinone ring of dibromophakellstatin in one step. Notably, it is possible to employ the reagent EtO2CNHOTs in a double function as a source of the electrophilic nitrene and of a dipolar carbamoyl component. Use of debrominated precursor dipyrrolopyrazinones leads to much higher anellation yields and allowed us to develop a second generation synthesis. The cytostatic activity of dibromophakellstatin is confirmed.     

Total synthesis of the marine metabolite (-)-clavosolide D

The first total synthesis of the marine natural product (-)-clavosolide D is described confirming the structure of the unsymmetrical 16-membered diolide glycosylated by permethylated d-xylose moieties. Following efficient assembly of the two tetrahydropyrans using stereoselective Prins cyclizations, the side chains were introduced via an allylation/isomerization/anti cyclopropanation sequence; the final macrolactonization step was achieved under Yamaguchi conditions.     

Total synthesis of the marine alkaloid (-)-lepadin B

An enantioselective total synthesis of (-)-lepadin B has been developed starting from (2S,4S)-2,4-O-benzylidene-2, 4-dihydroxybutanal. The key steps in the synthesis include the use of an aqueous intramolecular acylnitroso Diels-Alder reaction to afford the trans-1,2-oxazinolactam and Suzuki cross-coupling reaction to elaborate the (E,E)-octadienyl unit.     

Concise total synthesis of the marine natural product ageladine A

A total synthesis of ageladine A has been achieved by exploiting a Pictet-Spengler-type condensation between 2-aminohistamine and 4,5-dibromo-2-formylpyrrole as the key step.     

Intramolecular 1,3-diyl trapping reactions: Total synthesis of the marine natural product (d, 1)Δ9(12)-capnellene

An intramolecular 1,3-diyl trapping reaction is utilized in the key step of a total synthesis of the marine natural product Δ⁹⁽¹²⁾-capnellene.     

Total synthesis of (-)-13-oxyingenol and its natural derivative

Ring functionalization: the total synthesis of a natural derivative of (-)-13-oxyingenol, a potent anti-HIV diterpenoid, is reported. The key steps in this synthesis include a ring-closing olefin metathesis and a Mislow-Evans-type [2,3]-sigmatropic rearrangement. This synthesis provides access to (-)-13-oxyingenol and its natural derivative in 21 steps from a synthetic intermediate previously prepared by Kigoshi and co-workers.     

Total synthesis of the anticancer natural product OSW-1

The highly potent anticancer natural saponin OSW-1 has been successfully synthesized from commercially available 5-androsten-3beta-ol-17-one 79 in 10 operations with 28% overall yield. The key steps in the total synthesis included a highly regio- and stereoselective selenium dioxide-mediated allylic oxidation of 80 and a highly stereoselective 1,4-addition of alpha-alkoxy vinyl cuprates 68 to steroid 17(20)-en-16-one 12E to introduce the steroid side chain. This total synthesis demonstrated once again the versatile synthetic applications of alpha-halo vinyl ether chemistry developed in our laboratories.     

Total synthesis of (+)-(S)-angustureine and the determination of the absolute configuration of the natural product angustureine

Angustureine, isolated from the bark of Galipea officinalis Hancock, is a novel quinoline alkaloid with a n-pentyl side chain at the 2-position. The total synthesis of (+)-(S)-angustureine and a determination of the absolute configuration of the natural product angustureine were achieved using ring-closing metathesis (RCM) and the Mitsunobu reaction as key steps.     

Total synthesis of (-)-salinosporamide A

A concise and stereoselective total synthesis of (-)-salinosporamide A (1), a potent inhibitor of the 20S proteasome that is in clinical development as an anticancer drug candidate, has been accomplished in 14 steps with 19% overall yield from 4-pentenoic acid. Our synthesis features a stereoselective alkylation utilizing a chiral auxiliary, formation of a pyrrolidine unit, and oxidation of the pyrrolidine to a γ-lactam. To demonstrate the scalability of our synthesis, (-)-salinosporamide A has been synthesized on a gram scale.     

Total synthesis of (-)-callystatin A

[reaction: see text] The enantioselective synthesis of callystatin A is described. The pivotal step in the synthesis is the stereoselective aldol reaction that generates the beta-hydroxy ketone moiety. Utilizing the allylic strain within the ethyl ketone precursor, we were able to generate the all-syn configuration of callystatin A. For the construction of the two diene moieties, both a Heck coupling and a Wittig reaction were employed.